The growth of semiconductor III-V compounds by chemical vapor deposition (CVD) using organometallics and hydrides as elemental sources has recently developed into a viable process with many potential commercial applications. The metallo-organic chemical vapor deposition (MOCVD) process, based on the pyrolysis of alkyls of group-III elements in an atmosphere of the hydrides of group-V elements, is a common growth technique because it is well adapted to the growth of submicron layers and heterostructures.
Open-tube flow systems are used at atmospheric or reduced pressures in producing the III-V alloys. The process requires only one high-temperature zone for the in situ formation and growth of the semiconductor compound directly on a heated substrate.
Low pressure (LP-) MOCVD growth method offers an improved thickness uniformity and compositional homogeneity, reduction of autodoping, reduction of parasitic decomposition in the gas phase, and allows the growth of high-quality material over a large surface area. The LP-MOCVD technique has been successfully used to grow InAsSb/InAsSbP alloy on an InAs substrate. InAsSbP alloys, which are potentially useful materials both for heterojunction microwave and optoelectronic device applications can be grown by liquid-phase epitaxy (LPE), molecular-beam epitaxy (MBE), conventional vapor-phase epitaxy (VPE), as well as MOCVD.
The disadvantages of LPE include growth problems with InAsSbP alloys and potential nonuniform growth as well as melt-back effect. Molecular-beam epitaxy is a very expensive and complex process, and difficulties have been reported with p-type doping and with the growth of phosphorus-bearing alloys. Vapor-phase epitaxy disadvantages include potential for hillock and haze formation and interfacial decomposition during the preheat stage.
The technique of LP-MOCVD is well adapted to the growth of the entire composition range of InAsSbP layers of uniform thickness and composition on InAs substrates. This results first from the ability of the process to produce abrupt composition changes and second from the result that the composition and growth rate are generally temperature independent. It is a versatile technique, numerous starting compounds can be used, and growth is controlled by fully independent parameters.
Growth by MOCVD takes place far from a thermodynamic equilibrium, and growth rates are determined generally by the arrival rate of material at the growing surface rather than by temperature-dependent reactions between the gas and solid phases.
One of the key reasons for the usefulness of this method is the possibility of obtaining high-purity and therefore high-mobility InAsSbP. As long-wavelength 2-6 .mu.m InAsSbP electro-optical devices become more widely used, motivated by low fiber absorption and dispersion, high transmission through water and smoke, and greatly enhanced eye safety at wavelengths greater than 2 .mu.m, LP-MOCVD offers the advantages of smooth uniform surfaces, sharp interfaces (lower than 5 .ANG. for InAsSbP/InAs), uniformly lower background doping density, and economy of scale for large-area devices.
It is well known that the mid-infrared range from 3-5 .mu.m is very attractive for several spectroscopic applications including atmospheric trace gas analysis and medical diagnostics, because in this spectral region many atmospheric species have strong rotational, vibrational and overtone absorption bands. Unfortunately, the performance of narrow band-gap semiconductor lasers is strongly influences by Auger processes and carrier leakage effects.
The high quality of double heterostructure laser diodes based on the InAs.sub.0.95 Sb.sub.0.05 /InAs.sub.0.40 Sb.sub.0.22 P.sub.0.38 alloy on InAs substrate (100) grown by MOCVD is known which shows low threshold current density and a high output power. However, for the InAsSb/InAsSbP system it would be desirable to tune the system to emit a specific wavelength within that range.